An essential element in most orthodontic treatment is the use of some device to deliver a force to retract the maxilla. The function of such devices is to effect a relative or absolute posterior displacement of the maxilla and the maxillary dentition within the developing and expanding skull. Many investigators and clinicians consider the achievement of normal jaw to jaw relationships by such restraint of the forward development of the maxilla to be primary biological gain produced by orthodontic treatment. Considerable disagreement exists as to which of several vectors of force is the most desirable and the most effective. The present study is intended to provide clinical useful answers by rigorous quantitative determinations of the actual effects of clinical treatment using each of four different force vectors Records will be examined of samples of patients treated by several skilled clinicians, each using the method of own choice. The primary information source will be from standardized lateral skull X-ray films. Data is extracted from these films using a computer-aided method known as the University of California Combined Head Film Analysis.